A direct current, electrostatic thermionic electron gun is formed from several parts: a hot cathode, which is heated to create a stream of electrons via thermionic emission, electrodes generating an electric field which focus the beam (such as a Wehnelt cylinder), and one or more anode electrodes which accelerate and further focus the electrons. A large voltage between the cathode and anode accelerates the electrons. A repulsive ring placed between them focuses the electrons onto a small spot on the anode at the expense of a lower extraction field strength on the cathode surface. Often at this spot is a hole so that the electrons that pass through the anode form a collimated beam and finally reach a second anode called a collector. This arrangement is similar to an Einzel lens.

The most common use of electron guns is in cathode ray tubes, which were widely used in computer and television monitors. An electron gun can also be used to ionize particles by adding or removing electrons from an atom. This technology is sometimes used in mass spectrometry in a process called electron ionization to ionize vaporized or gaseous particles. More powerful electron guns are used for welding, metal coating, 3D metal printers, metal powder production and vacuum furnaces.